This article investigates the impact of NATO's 1999 intervention in Kosovo on the notion of sovereignty as responsibility. It argues that the intervention provided an important catalyst that brought to light a broad consensus about sovereignty as responsibility and highlighted areas in need of refining. International debate about the intervention brought to light a broad consensus around the principle that sovereigns do not have unlimited rights to treat their citizens however they please but highlighted concerns about the modalities of operationalizing such a principle. Not least, states were concerned about the potential for unilateral armed intervening. As such, the debate sparked by NATO's intervening revolved more around second-order questions about the authority to intervene and prudential questions about its impact on regional stability than on the question of whether international society should be engaged in a domestic humanitarian crisis. This pointed to the idea that a grand consensus on sovereignty as responsibility might be possible if its scope for justifying armed intervention was constrained to only those cases where the Security Council authorizes action. It was precisely this formula that emerged from the 2005 World Summit.